Within the field of chip removing or cutting machining of, above all, blanks of metal, a continuous development is going on with the purpose of making more effective not only the capacity of the tools to carry out the machining in a fast and accurate way, but also the manufacture of the different parts of the tools in the form of basic bodies (holders) and replaceable cutting inserts. A trend is to improve the machining results in respect of the precision and surface finish, which requires that the active edge of the cutting insert obtains an exact, predetermined position in relation to the basic body. In many applications, the requirements of position precision are extreme. Another trend is to reduce the costs for the manufacture of the tools. This has, among other things, implied that the cutting inserts made of cemented carbide, which are the most commonly occurring on the market, have got a better and better dimensional accuracy already in connection with the compression moulding and sintering. In order to obtain good precision of the cutting inserts, it was previously necessary to subject the same to expensive grinding operations, but by means of the improved compression-moulding and sintering technique it has become possible to use directly pressed, i.e., unground cutting inserts in more and more applications. However, such development has merely advanced such that the tool constructor still has to allow for a dimensional variation on the order of (+/−) 0.5% of the nominal dimension of the cutting insert. This means that the active edge of the cutting insert very well may end up in the desired position, in which case the outcome of the insert production is good, but when the outcome is worse (so far that the cutting insert has swollen and become longer, or shrinked and become shorter than intended), the position of the cutting edge in relation to the basic body may deviate to such a high extent from the desired position that the machining precision will be unsatisfactory.
In older tools, the exact position of the active cutting edge was determined by the distance between the edge and a clearance surface positioned on the opposite side of the cutting insert, which clearance surface was pressed against a co-operating, rear or inner support surface in the insert seat of the basic body. In this case—when the rear clearance surface of the cutting insert formed a reference point that determined the space position of the front edge—the position precision of the edge could become catastrophically poor, provided that the cutting insert was not ground, because the distance between the active edge and the opposite clearance surface is—in this connection—considerable, in particular when the tools and the cutting inserts are big. Recently, so-called serration connecting surfaces have been developed as means for holding the cutting inserts. In such a way, the position precision of the cutting edge has been possible to be redoubled (i.e. the tolerance is halved), more precisely by the fact that a central ridge on the serration connecting surface of the cutting insert is chosen as a reference point for the position of the cutting edge. By the fact that the central ridge is halfway between opposite sides/edges of the cutting insert, the distance is halved between the active cutting edge and the locating reference point, with the ensuing halving of the tolerance errors. However, also this position precision has been unsatisfactory in many of the applications that require better and better machining results.
With the purpose of managing the above-mentioned shortcomings of the tools that make use of serration connecting surfaces in the interface between the cutting insert and the insert seat of the basic body, International Patent Application Publication No. WO 2005/072898discloses making the parallel ridges and grooves, which together form the insert seat or serration connecting surface of the basic body, in such a way that the width of the grooves progressively increases in the direction from a front groove toward a rear one, the front groove forming the reference locus from which possible form defects can be distributed backwardly or inwardly toward the other grooves. This means that the distance between the active edge of the cutting insert and the fixed reference locus in the form of the front groove is reduced to a fraction of the length of the cutting insert. In other words, the impact of the form defects on the position of the edge is reduced to a corresponding extent. However, even if this solution has given promising results, the same has turned out to have certain drawbacks. One of these is that the great number of ridges on the connecting surface of the cutting insert complicates the manufacture of the cutting inserts. More precisely, form defects may manifest themselves in small irregularities in the planar flank surfaces of the ridges, the irregularities occurring randomly on different ridges and on different parts of the same. When the outcome of the manufacture is bad, such irregularities on the numerous ridges may cause the ridges not to engage correctly with the grooves in the connecting surface of the basic body, in spite of the grooves being formed with progressively increasing widths. Furthermore, the front ridge of the cutting insert, positioned closest to the edge, may jam in the appurtenant groove in the connecting surface of the basic body, whereby the cutting insert is locked so that it cannot tilt down freely into the desired position. To this, it should be added that the interface in question, which makes use of true serration connecting surfaces, only can transfer force in a single coordinate direction, i.e. perpendicularly to the length extension of the ridges.
International Patent Application Publication No. WO 02/055243 discloses a known tool, the cutting insert and basic body of which are connected with each other via serration connecting surfaces, the ridges of which are formed with thin, string-like material portions, which project in relation to the otherwise planar flank surfaces of the ridges. However, the purpose of these material strings is to predetermine the locus of the contact between co-operating flank surfaces, but not to allow free adjustment of the contact places upward or downward along the surfaces.
The present invention aims at obviating the above-mentioned drawbacks of previously known cutting tools of the type initially mentioned, and at providing an improved cutting tool. Therefore, an object of the invention, in a first aspect, is to provide a cutting tool that allows the use of unground cemented-carbide inserts, the precision of which, in respect of the position of the active cutting edge in relation to the basic body, is optimum.
Another object of the invention is to provide a tool, the interface of which between the cutting insert and the basic body can transfer forces in two different coordinate directions, e.g., radially as well as axially.
Yet another object of the invention is to simplify and cheapen the manufacture of, primarily, the cutting inserts.
Still another object is to provide a tool that allows the use of indexable cutting inserts having a plurality of edges, without the edges—in spite of the plurality thereof—running the risk of being incorrectly positioned.
It is also an object to provide a tool, the interface of which between the cutting insert and basic body allows the use of cutting inserts having most dissimilar basic shapes.
Thus, the cutting inserts should be possible to have a polygonal basic shape, such as triangular, square, parallelepipedic, rhombic, pentagonal, hexagonal, septagonal, octagonal, etc., or be round, preferably circular. Furthermore, the cutting insert should be fixable in the insert seat by means of arbitrary means, such as screws, clamps, lever mechanisms, eccentric mechanisms, etc.